During operations to drill and complete an oil or gas well, debris such as metal cuttings, broken metal or composite parts, pieces of rock, sand, and other unwanted material may obstruct a wellbore and prevent access required for further operations in the wellbore. The debris may have accumulated in the wellbore due to normal drilling operations or due to the milling of objects such as packers, plugs or stuck tools.
A common method for wellbore debris removal involves a bottom-hole assembly (“BHA”) employing reverse circulation of pumped fluid, a nozzle or narrow fluid passageway, and a debris collection chamber. Using normal circulation, pumped fluid flows from a pump at the surface through a central pipe bore, such as through a work string and any distally adjoining equipment, exiting the central pipe bore at the bottom of the wellbore, and returning up the annular space between the wall of the wellbore and the work string or adjoining equipment to the surface. In contrast, when using reverse circulation, the supplied fluid is diverted out of the central pipe bore and into the annular space before the fluid reaches the bottom of the wellbore. The diverted fluid flows through one or more nozzles or narrow fluid passageways that accelerate the fluid and induce a pressure drop as the diverted fluid flows toward the annular space. The diverted fluid flows down the annular space to the distal end of a debris collection assembly. This fluid flow agitates debris near this distal end, entrains the debris, and carries the debris into a collection chamber that includes check valves and a screen to capture the debris. In the vicinity of the upper portion of the collection chamber, the debris-entrained fluid passes through a screen or filtering mechanism. The filtering mechanism cleans the fluid of debris to a certain extent and the cleaned fluid moves on through passageways to the annular space and down to the distal end of a debris collection assembly. When the operation is complete, the bottom hole assembly is pulled to the surface and the collection chamber is emptied of collected debris.
In current reverse circulation systems, diverted fluid flows through one or more nozzles or narrow fluid passageways that accelerate the fluid and induce a pressure drop, creating suction to urge debris-entrained return fluid toward the low pressure area generated by the nozzle. This suction effect draws debris into a collection chamber for capture and subsequent extraction.
However, haphazard placing of a low pressure, high velocity flow area in relation to return fluid effuse ports or passages—for example, in the annular space—achieves inefficient suction. Further, current implementations emphasize creating a decrease in pressure and not on making any purposeful use of the kinetic energy inherent in increased fluid velocity. For example, in situations involving clogged wellbores and few or one collection chamber segments, more kinetic energy to entrain debris would be helpful. Another case of annular space fluid velocity playing a key role occurs in the event the BHA is deployed with the work string being comprised of coiled tubing rather than straight tubular segments. The nature of coiled tubing operations make it likely that the collection chamber would have very limited segments and additionally that the BHA might not have a means of rotation.
In addition, suction achieved using a low pressure flow area in the annular space cannot be adjusted for wellbore conditions or suboptimal fluid pumping capacity.
As the foregoing illustrates, what is needed in the art is an improved suction apparatus that can be customized to a particular drilling situation while remaining strong enough to withstand wellbore operations.